1. Field of the Invention
This invention relates to a method of gas reaction process control for carrying out various gas reaction processes including etching of semiconductor substrates, various thin films and other specimens, as well as oxidation and nitridation.
2. Prior Art Statement
The devices often used when conventionally carrying out dry etching of semiconductor specimens include plasma etching devices and reactive ion etching (RIE) devices, for example.
Yet in these devices, etching is carried out by applying a high-frequency voltage across a pair of parallel plate electrodes facing each other in a vacuum chamber, so that a specimen attached in advance to the surface of one of the electrodes is directly exposed to the plasma thus generated. Thus the ions in the plasma collide with the surface of the specimen at high energies, often causing damage.
To remedy this situation and eliminate these types of defects, plasma etching devices using ECR (electron cyclotron resonance) ion sources have been proposed. (For example, Japanese Pat. Public Disclosure No. 59-127832.)
In these devices, microwaves and a static magnetic field are applied to low-pressure gas in a plasma generation section provided at a location separate from where the specimen to be processed is held. By causing the electrons in the plasma thus generated to undergo cyclotron motion, the ionization rate within the plasma is increased. Once a high-density, long-lived plasma is generated, it is transported to the location at which the specimen is held, and the etching process is carried out there.
Using such ECR-type plasma etching devices, because the specimen is not located in the environment of plasma generation, the problem of damage to the specimen surface from direct ion collisions is solved.
However, instead, particularly when there is a thin insulating film on the surface of the specimen, there occurs a phenomenon which causes degradation of this insulating film.
The inventors of this invention studied the causes of this phenomenon in an effort to remedy this situation. As a result, they found that the ions and electrons and such in the plasma gas were accumulating on the surface of the specimen, creating a large difference in electric potential between the front and back surfaces of the specimen, and that the deterioration of the thin insulating film was due to this difference in electric potential.
In addition, as a result of obtaining this knowledge, it was found that this problem with specimen surface potential is not limited to ECR-type devices as described above, but rather is a problem common to all devices which carry out some kind of gas reaction processing such as etching as described above, as well as oxidation, nitridation and other processes accomplished by generating plasma gas at a location separate from where the specimen is held, and selectively transporting the dissociated ions, electrons or radicals (free radicals: excited atoms or molecules) to the surface of the specimen.